1. Field of the Invention
The present invention relates to methods and apparatus for setting and unsetting an inflatable packer in a subterranean oil or gas well by using coiled tubing or remedial tubing for pumping fluids to the packer. More particularly, the invention relates to improved methods and apparatus for retrieving a packer sized to set in a casing through a relatively small diameter production tubing.
2. Description of the Prior Art
Those skilled in the art relating to remedial operations associated with drilling, production, and completion of subterranean oil and gas wells have long utilized threaded or coupled remedial tubing inserted through production tubing for pumping fluids from the surface to one or more inflatable packers. More recently, continuous coiled remedial tubing has frequently replaced threaded or coupled tubing to pass fluid to a packer, since coiled tubing may be more rapidly inserted into the well, and may be easily passed through production tubing and related downhole equipment because its diameter is consistently the same size.
Typical remedial coiled tubing apparatus is described in the 1973 Composite Catalog of Oil Field Equipment and Services, at page 662 (Gulf Publishing Co., Houston, Texas), and manufactured by Bowen Tools, Inc. of Houston, Texas. Apparatus relating to this coiled tubing technique is more particularly described in U.S. Pat. Nos. 3,182,877 and 3,614,019.
The need frequently arises in remedial or stimulation operations to pass an inflatable packer through small diameter restrictions, e.g. 31/2 inch production tubing, set the packer in relatively large diameter casing, e.g., 7 inch casing, unset the packer, and then retrieve the packer to the surface through the small diameter tubing. Recent advances, such as those disclosed in U.S. Pat. No. 4,349,204, enable inflatable packers to pass through such small diameter tubing, effectively seal with a larger diameter casing, and then be retrievable to the surface through the small diameter tubing.
A significant problem in the art concerns retrieval of the packer and the packer actuation apparatus, side pocket mandrels and similar tooling interconnected to the packer. During retrieval, if the packer or tooling get "hung up" on a restriction and conventional threaded remedial tubing is utilized to supply fluid to the packer, the remedial tubing may be rotated to "free" the mismatch and enable the equipment to be removed through the production tubing. This technique is not utilized with coiled tubing, however, since the coiled tubing cannot be effectively rotated. One technique for alleviating this problem is to attach a partial cone-shaped end to the lower end of the coiled tubing to permit the tubing to slide off the obstruction. Another technique alters the position of the end of the tubing with cams for producing a rotary motion in response to longitudinal motion on the tubing, as disclosed in U.S. Pat. No. 3,912,014.
Another problem associated with the prior art concerns the interconnection of the coiled tubing with the downhole packer actuation assembly. Inflatable packers may be unset by pulling upwardly on the coiled tubing. Set screws have been utilized to connect the coiled tubing to the packer actuation assembly, and such set screws tend to loosen during downhole operations, allowing the tubing to pull away from the packer actuation assembly. Also, coiled tubing has broken off downhole above the packer actuation assembly/coiled tubing connection. In either event, retrieval of the packer actuation assembly, the packer, and interconnected downhole equipment is then a major problem, often requiring sophisticated fishing tool retrieval techniques.